1. Field of the Invention
The invention pertains to a novel stratospheric vehicle, novel airship gore and energy producing covering for high altitude platforms and method of producing the novel flexible energy producing covering. More particularly the invention pertains to a three-dimensional flexible covering which incorporates flexible solar cells as part of the outer layer of a bonded flexible envelope for high altitude airships, dirigibles and other such stratospheric, near space and space vehicles. The novel flexible energy producing bonded covering is a lightweight thin film material, typically 300 to 400 microns thick and weighs about 300 to 600 grams per square meter.
The novel lightweight flexible energy producing material is particularly suited for aircraft, spacecraft and lighter-than-air vehicles such as dirigibles, blimps and balloons constructed to operate in the stratosphere, at the threshold of space and in space. The energy producing skin is capable of converting sunlight into electricity and operate at low and high voltages of 40 to 6,000 and preferably 100 to 600 volts while having a total skin thickness of a few hundred microns. The invention achieves its advantages by combining thin plastic film flexible solar cells with thin film and fabric airship materials to produce a lightweight, durable, energy producing flexible covering particularly suited for airship technology.
The construction and design of high altitude platforms and airships involve a series of considerations all of which require a consideration of weight. The greater the weight, the greater the volume of lift gas required which increase the amount of covering necessary to contain the lift gas which results in a further increase in weight. These increases in weight and volume also impose additional power requirements to maneuver the airship or to place a vehicle in space or at the threshold of space. As a result a lightweight high energy producing material breaks the volume weight power cycle and allows a stratospheric vehicle to operate at a higher altitude and in space and to more efficiently gather and utilize energy.
As used herein the term vehicle and high altitude platform includes airships and other vehicles that operate in the stratosphere, threshold of space and in space which require a lightweight, energy producing material to maintain a given altitude or orbit or require lightweight materials for launching into space.
The flexible solar cell energy producing cover is bonded to the substrate of the flexible airship envelope while electrical contacts are being made to a conductive conduit carried between layers which also becomes part of the structural strength of the novel flexible energy producing covering. In one embodiment of the invention a special electrically conductive fabric layer is employed allowing the fabric substrate to electrically conduct electrical current along the length of the airship through the warp of the fabric while adding structural strength to the novel energy producing material. In another embodiment of the invention the electrical conduit provided by the fabric warp is combined with a conductive conduit in the form of a metallic ribbon or electrically conductive fibers sandwiched and electrically insulated by a flexible non-conductive polymer bonding adhesive.
The airship substrate may also be gas impervious or slightly gas pervious depending upon the particular method of the invention selected for producing the novel flexible energy producing covering. In the preferred application of the invention the airship substrate is substantially gas impervious and the method of the invention provides for the joining of the flexible solar cell layer with a non-conductive adhesive under heat, pressure and a vacuum to prevent the presence of small air bubbles from being trapped in the adhesive layer and rupturing or interfering with the integrity of the system in stratospheric applications.
In applications where the airship substrate is slightly gas pervious the flexible solar cell layer can be joined with the airship substrate with a flexible polymer adhesive under heat and pressure without a vacuum since small air bubbles upon expansion in the stratosphere can migrate into and through the gas pervious airship substrate. In the preferred embodiment the laminating process is performed under heat, pressure and a vacuum to remove air and provide a novel flexible and resilient energy producing covering particularly suited to high altitude and space vehicles.
2. Description of Related Art Including Information Disclosed Under 37 C.F.R. 1.97 and 37 C.F.R. 1.98
The sun is an ideal power source for long duration (one year or longer) stratospheric airships because of the lack of moisture and thin air in the stratosphere. At approximately 20-50 kilometers (12-31 miles), sunlight is a very strong, predictable source of energy. The major reasons solar power has not been utilized on airships are traditional, rigid solar cells are heavy and difficult to incorporate onto an airship envelope and the added weight of the solar cell added to the weight of the covering limits the absolute altitude at which the airship can operate with a given amount of lift gas and engine power.
Rigid solar cells are heavy because they are made with a glass substrate which is one of the heavier materials available and are usually mounted on stiff panels to prevent them from being twisted and cracked since they are rarely more than a few microns (thousandth of an inch) thick. Rigid solar cell arrays have been calculated to produce only about half the power for the same mass than lighter flexible solar cell arrays produce. This is because flexible solar cell arrays are made from thin layers of amorphous silicon deposited onto plastic film. Not only are these materials lighter than crystalline silicon bonded to glass, but they are inherently flexible and do not require stiff panels to protect them from twisting and cracking. This invention does not pertain to mounting rigid solar cells to an airship but instead to mounting flexible solar cells to an airship. However the problems encountered in mounting rigid or flexible solar cells to an airship are similar.
One common problem to mounting solar cells to airships is weight and particularly the added weight of the special mounting devices and other items that are required to mount rigid solar cell arrays onto the thin, curved flexible skin of an airship. While flexible solar cells are lighter there remains the common problem of expandability which is comparable to attaching small mirrors or strips of plastic to a balloon and then adding wiring and electrical connector and hardware between the mirrors or strips of plastic. These resulting rigid panels have to be attached with special mounting devices and electrical connectors to compensate for the flexing and this increases the weight without increasing power output.
A further problem in addition to weight is that large panels of rigid solar cells or flexible solar cells mounted on the surface of the airship are much like adding flat windowpanes or adding a covering to a covering that increases the size, drag and power required of the propulsion system. Such flat windowpane panels or added covering increases drag and impairs maneuverability and requires more power to propel the airship. Reducing the size of the panels and mounting more of them on the airship surface like mosaic tile is impractical as it adds additional weight by virtue of the additional wiring and electrical connectors required to connect the panels to the airship skin. Examples of prior art applications of rigid solar cells in panels and arrays with supporting frames for carrying the rigid cells is illustrated by Stark U.S. Pat. No. 4,364,532 and the attachment of solar cells to the flexible envelope of an airship is illustrated in Nakada U.S. Pat. No. 5,348,254.
Nakada U.S. Pat. No. 5,348,254 provides a specially fabricated single semi-circular solar cell that appears to be attached to the flexible envelope of the airship. In practice such an attachment of a rigid solar cell to a flexible envelope for a long duration application would result in delamination or shattering the solar cell as a result of the repeated flexing of the flexible airship substrate envelope. In Stark U.S. Pat. No. 4,364,532 the panels appear to be placed on the outside of the airship and appear to be held by frames and not attached directly to the envelope. This arrangement prevents delamination and shattering of the solar cell but at the expense of the aerodynamic characteristics of the airship and at the possible expense of the integrity of the airship envelope at the interface between the rigid frame and the thin flexible airship skin.
Other prior art such as Wurst, et al. U.S. Pat. No. 5,518,205 utilize a rigid wing or support structure of limited expandability as a substrate for a solar cell array for a high altitude platform. In Wurst, et al. '205 the rigid solar cells are placed upon a rigid airfoil shaped wing which obviates the problem of having a three-dimensional flexible substrate which expands and contracts underneath a rigid solar cell. Wurst, et al. '205 like the other prior art does not incorporate the solar cells directly into a flexible envelope of the high altitude platform.
Weinert U.S. Pat. No. 4,768,738 describes a special thread of a conductive fiber that is woven into a flexible solar skin for absorbing radiant energy and converting it into electricity. Weinert does not specifically disclose the nature of the special fabric nor does Weinert describe the fabric as being made from flexible solar cells. Weinert does not describe the novel product or process of the invention of incorporating flexible solar cells into the thin flexible skin of high altitude airships or dirigibles.
Other prior art such as Tanzilli, et al. U.S. Pat. No. 5,427,629 pertains to a silicon carbide cover for covering traditional rigid solar cells for increasing the absorptivity of useful light. Toyama, et al. U.S. Pat. No. 5,500,055 pertains to the utilization of an irregular transparent conductive layer on a metallic substrate solar cell to increase the efficiency of the solar cell. The processing of traditional rigid silicon solar cells does not provide a flexible solar cell attached to a three dimensional flexible substrate for providing energy for high altitude platforms. Goodfellow U.S. Pat. No. 3,974,989, Abildskov U.S. Pat. No. 5,533,693 and Pavlecka U.S. Pat. No. 4,208,027 pertain to lighter-than-air fabric materials and for the lightweight connection of structural members to sheets or gores of dirigibles. These references do not include the utilization of flexible solar cells or teach or suggest the novel process of the invention.
Flexible solar cells that may be used in accordance with the invention are available in a variety of designs and configurations. For stratospheric applications flexible solar cells should include solar cells having both electrodes extending through the back of the solar cell as described in U.S. patents to Hanoka U.S. Pat. No. 5,478,402, Safir U.S. Pat. No. 5,665,175, Nishiura, et al. U.S. Pat. No. 4,609,770, Yoshida U.S. Pat. No. 5,626,686 and Kawama, et al. U.S. Pat. No. 5,665,607. Solar cells having both electrodes extending through the flexible solar cell are utilized in stratospheric and space applications since the power generating surface occupied by the solar cell is unencumbered by electrodes thereby saving surface area and weight and all connections can be insulated and shielded between the flexible solar cell layer and the airship substrate employing the flexible non-conductive adhesive.
The known flexible solar cell prior art does not provide for the direct application of flexible solar cells directly to the airship skin or airship gore and make electrical connections between layers as provided in accordance with the present invention. The prior art also does not provide for conductive conduits disposed intermediate the flexible solar cell airship skin and the substrate in which the conductive conduits are insulated by the flexible non-conductive adhesive nor does the prior art provide for the application of conductive adhesive in localized contact areas to insure a good electrical contact between the solar cell and conductive conduit. The prior art such as Dougherty U.S. Pat. No. 5,264,285 teaches flexible polymer adhesives and Walker, et al. U.S. Pat. No. 4,067,764 teaches the use of a vacuum in laminating solar cells. Neither of these references show or suggest the novel method of bonding a gas impervious flexible solar cell layer to flexible airship substrate in accordance with the invention.
The flexible solar cell layer and flexible substrate of the airship are bonded together using a flexible non-conductive polymer adhesive utilizing heat and pressure and in the preferred embodiment a vacuum. The novel process eliminates the requirement for the use of a vacuum in bonding the flexible solar cell with the flexible airship substrate where the flexible airship substrate is gas pervious. In applications where a gas pervious airship substrate is utilized small bubbles of gas or air caught between layers when expanded in the stratosphere are able to migrate through the gas pervious substrate into the interior of the airship without rupturing the airship skin on the flexible solar cell layer encapsulating the novel flexible solar ship. In the preferred embodiment of the invention in stratospheric and near space applications a vacuum is employed with or without a gas pervious airship substrate to prevent air or a gas from being trapped between the flexible airship substrate and the gas impervious flexible solar cell layer.
Unlike the prior art the invention provides for a flexible energy producing material having a flexible solar cell outer layer bonded to a flexible inner layer of fabric or plastic with one or more conductive conduits disposed between a flexible non-conductive polymer adhesive and the flexible solar cell outer layer and the fabric or plastic inner layer. The flexible inner layer may be gas-impervious or slightly gas pervious depending upon the method of the invention utilized for bonding the non-conductive polymer adhesive to the flexible solar cell outer layer and the flexible fabric or plastic inner layer. Conductive conduits between the layers are shielded and electrically insulated in the non-conductive adhesive or in the fabric layer and non-conductive adhesive.
Unlike the prior art the novel invention incorporates a flexible solar cell on portions of the airship gore as part of the envelope material of the airship which in the preferred embodiment provides three-dimensional flexibility and conforms exactly to the aerodynamic curves of the airship without having impermissible air between the layers. In the preferred embodiment, the novel invention includes specialized electrically conductive warp threads in a special gore substrate fabric to conduct solar generated electricity in the novel airship skin. In all embodiments of the invention a novel thin film flexible energy producing covering of paper thin thicknesses is provided for stratospheric applications to rigid, semi-rigid and three-dimensional expandable substrates.